Effect of the long-term administration of corticotropin-releasing factor on the pituitary-adrenal and pituitary-gonadal axis in the male rat

Unraveling corticotropin-releasing factor family-orchestrated signaling and function in both sexes

Stress responses to physical, psychological, environmental, or cellular stressors, has two arms: initiation and recovery. Corticotropin-releasing factor (CRF) is primarily responsible for regulating and/or initiating stress responses via, whereas urocortins (UCNs) are involved in the recovery response to stress via feedback inhibition. Stress is a loaded, polysemous word and is experienced in a myriad of ways. Some stressors are good for an individual, in fact essential, whereas other stressors are associated with bad outcomes. Perceived stress, like beauty, lies in the eye of the beholder, and hence the same stressor can result in individual-specific outcomes. In mammals, there are two main biological sexes with reproduction as primary function. Reproduction and nutrition can also be viewed as stressors; based on a body of work from my laboratory, we propose that the functions of all other organs have co-evolved to optimize and facilitate an individual's nutritional and reproductive functions. Hence, sex differences in physiologically relevant outcomes are innate and occur at all levels- molecular, endocrine, immune, and (patho)physiological. CRF and three UCNs are peptide hormones that mediate their physiological effects by binding to two known G protein-coupled receptors (GPCRs), CRF1 and CRF2. Expression and function of CRF family of hormones and their receptors is likely to be sexually dimorphic in all organs. In this chapter, based on the large body of work from others and my laboratory, an overview of the CRF family with special emphasis on sex-specific actions of peripherally expressed CRF2 receptor in health and disease is provided.

Sex differences in binge-like EtOH drinking, corticotropin-releasing hormone and corticosterone: effects of β-endorphin

Binge drinking is an increasingly common pattern of risky use associated with numerous health problems, including alcohol use disorders. Because low basal plasma levels of β-endorphin (β-E) and an increased β-E response to alcohol are evident in genetically at-risk human populations, this peptide is thought to contribute to the susceptibility for disordered drinking. Animal models suggest that the effect of β-E on consumption may be sex-dependent. Here, we studied binge-like EtOH consumption in transgenic mice possessing varying levels of β-E: wild-type controls with 100% of the peptide (β-E +/+), heterozygous mice constitutively modified to possess 50% of wild-type levels (β-E +/-) and mice entirely lacking the capacity to synthesize β-E (-/-). These three genotypes and both sexes were evaluated in a 4-day, two-bottle choice, drinking in the dark paradigm with limited access to 20% EtOH. β-E deficiency determined sexually divergent patterns of drinking in that β-E -/- female mice drank more than their wild-type counterparts, an effect not observed in male mice. β-E -/- female mice also displayed elevated basal anxiety, plasma corticosterone and corticotropin-releasing hormone mRNA in the extended amygdala, and all of these were normalized by EtOH self-administration. These data suggest that a heightened risk for excessive EtOH consumption in female mice is related to the drug's ability to ameliorate an overactive anxiety/stress-like state. Taken together, our study highlights a critical impact of sex on neuropeptide regulation of EtOH consumption.

The impact of stress on body function: A review

Any intrinsic or extrinsic stimulus that evokes a biological response is known as stress. The compensatory responses to these stresses are known as stress responses. Based on the type, timing and severity of the applied stimulus, stress can exert various actions on the body ranging from alterations in homeostasis to life-threatening effects and death. In many cases, the pathophysiological complications of disease arise from stress and the subjects exposed to stress, e.g. those that work or live in stressful environments, have a higher likelihood of many disorders. Stress can be either a triggering or aggravating factor for many diseases and pathological conditions. In this study, we have reviewed some of the major effects of stress on the primary physiological systems of humans.

A Mechanistic Basis for the Beneficial Effects of Caloric Restriction On Longevity and Disease: Consequences for the Interpretation of Rodent Toxicity Studies

Caloric restriction in rodents has been repeatedly shown to increase life span while reducing the severity and retarding the onset of both spontaneous and chemically induced neoplasms. These effects of caloric restriction are associated with a spectrum of biochemical and physiological changes that characterize the organism's adaptation to reduced caloric intake and provide the mechanistic basis for caloric restriction's effect on longevity. Here, we review evidence suggesting that the primary adaptation appears to be a rhythmic hypercorticism in the absence of elevated adrenocorticotropin (ACTH) levels. This characteristic hypercorticism evokes a spectrum of responses, including reduced body temperature and increased metabolic efficiency, decreased mitogenic response coupled with increased rates of apoptosis, reduced inflammatory response, reduced oxidative damage to proteins and DNA, reduced reproductive capacity, and altered drug-metabolizing enzyme expression. The net effect of these changes is to (1) decrease growth and metabolism in peripheral tissues to spare energy for central functions, and (2) increase the organism's capacity to withstand stress and chemical toxicity. Thus, caloric restriction research has uncovered an evolutionary mechanism that provides rodents with an adaptive advantage in conditions of fluctuating food supply. During periods of abundance, body growth and fecundity are favored over endurance and longevity. Conversely, during periods of famine, reproductive performance and growth are sacrificed to ensure survival of individuals to breed in better times. This phenomena can be observed in rodent populations that are used in toxicity testing. Improvements over the last 30 years in animal husbandry and nutrition, coupled with selective breeding for growth and fecundity, have resulted in several strains now exhibiting larger animals with reduced survival and increased incidence of background lesions. The mechanistic data from caloric restriction studies suggest that these large animals will also be more susceptible to chemically induced toxicity. This creates a problem in comparing tests performed on animals of different weights and comparing data generated today with the historical database. The rational use of caloric restriction to control body weight to within preset guidelines is a possible way of alleviating this problem.

Glucocorticoid Regulation of Reproduction

It is well accepted that stress, measured by increased glucocorticoid secretion, leads to profound reproductive dysfunction. In times of stress, glucocorticoids activate many parts of the fight or flight response, mobilizing energy and enhancing survival, while inhibiting metabolic processes that are not necessary for survival in the moment. This includes reproduction, an energetically costly procedure that is very finely regulated. In the short term, this is meant to be beneficial, so that the organism does not waste precious energy needed for survival. However, long-term inhibition can lead to persistent reproductive dysfunction, even if no longer stressed. This response is mediated by the increased levels of circulating glucocorticoids, which orchestrate complex inhibition of the entire reproductive axis. Stress and glucocorticoids exhibits both central and peripheral inhibition of the reproductive hormonal axis. While this has long been recognized as an issue, understanding the complex signaling mechanism behind this inhibition remains somewhat of a mystery. What makes this especially difficult is attempting to differentiate the many parts of both of these hormonal axes, and new neuropeptide discoveries in the last decade in the reproductive field have added even more complexity to an already complicated system. Glucocorticoids (GCs) and other hormones within the hypothalamic-pituitary-adrenal (HPA) axis (as well as contributors in the sympathetic system) can modulate the hypothalamic-pituitary-gonadal (HPG) axis at all levels-GCs can inhibit release of GnRH from the hypothalamus, inhibit gonadotropin synthesis and release in the pituitary, and inhibit testosterone synthesis and release from the gonads, while also influencing gametogenesis and sexual behavior. This chapter is not an exhaustive review of all the known literature, however is aimed at giving a brief look at both the central and peripheral effects of glucocorticoids on the reproductive function.

Protective effect of sex on chronic stress- and depressive behavior-induced vascular dysfunction in BALB/cJ mice

The presence of chronic, unresolvable stresses leads to negative health outcomes, including development of clinical depression/depressive disorders, with outcome severity being correlated with depressive symptom severity. One of the major outcomes associated with chronic stress and depression is the development of cardiovascular disease (CVD) and an elevated CVD risk profile. However, in epidemiological research, sex disparities are evident, with premenopausal women suffering from depressive symptoms more acutely than men, but also demonstrating a relative protection from the onset of CVD. Given this, we investigated the differential effect of sex on conduit artery and resistance arteriolar function in male and female mice following 8 wk of an unpredictable chronic mild stress (UCMS) protocol. In males, plasma cortisol and depressive symptom severity (e.g., coat status, anhedonia, delayed grooming) were elevated by UCMS. Endothelium-dependent dilation to methacholine/acetylcholine was impaired in conduit arteries and skeletal muscle arterioles, suggesting a severe loss of nitric oxide bioavailability and increased production of thromboxane A2 vs. prostaglandin I2 associated with elevated reactive oxygen species (ROS) and an increased level of systemic inflammation. Endothelium-independent dilation was intact. In females, depressive symptoms and plasma cortisol increases were more severe than in males, although alterations to vascular reactivity were blunted, including the effects of elevated ROS and inflammation on dilator responses. These results suggest that compared with males, female rats are more susceptible to chronic stress in terms of the severity of depressive behaviors, but that the subsequent development of vasculopathy is blunted owing to an improved ability to tolerate elevated ROS and systemic inflammatory stress.

Gender differences in serum testosterone and cortisol in patients with major depressive disorder compared with controls

OBJECTIVE

Testosterone may have a role distinct from cortisol in the pathophysiology of depression. The hypothalamus-pituitary-adrenal (HPA) axis affects the functions of sex steroid hormones through interaction with corticotropin-releasing hormone (CRH) and gonadotropin-releasing hormone (GnRH). The objective of this study was to investigate differences in serum levels of testosterone and cortisol in male and female patients with major depressive disorder (MDD).

METHODS

Participants included 87 inpatients with MDD at Juntendo University Koshigaya Hospital. Serum levels of testosterone and cortisol were assessed at admission. Matched controls included 128 healthy individuals. Data from MDD patients and controls were compared separately for men and women. Correlations between serum hormone levels and scores on the Hamilton Rating Scale for Depression (HAM-D) of patients were assessed by sex. Effects of various factors on testosterone and cortisol were analyzed using multiple regression analysis.

RESULTS

In male patients with MDD, a significant negative correlation was seen between testosterone levels and the "retardation" score of HAM-D. However, serum testosterone levels were not significantly different in either male or female MDD patients compared with controls. Serum testosterone was negatively associated with the number of depressive episodes in male patients with MDD. Serum cortisol levels in female patients were significantly increased compared with female controls with no significant correlations between cortisol levels and HAM-D scores.

CONCLUSIONS

The negative correlation between the sub-score of the HAM-D and testosterone may be associated with the biological pathophysiology of male depression. Findings of serum cortisol levels in women may suggest distinct characteristics of these hormones in men and women with MDD.

Effects of prolonged exendin-4 administration on hypothalamic-pituitary-adrenal axis activity and water balance

Exendin-4 (Ex-4) is a natural agonist of the glucagon-like peptide-1 (GLP-1) receptor, currently being used as a treatment for type 2 diabetes mellitus due to its insulinotropic properties. Previous studies have revealed that acute administration of both GLP-1 and, in particular, Ex-4 potently stimulates hypothalamic-pituitary-adrenal (HPA) axis activity. In this work, the effects of prolonged Ex-4 exposure on HPA function were explored. To this end, Sprague-Dawley rats were subjected to a daily regimen of two Ex-4 injections (5 μg/kg sc) for a minimum of 7 days. We found that subchronic Ex-4 administration produced a number of effects that resemble chronic stress situations, including hyperactivation of the HPA axis during the trough hours, disruption of glucocorticoid circadian secretion, hypertrophy of the adrenal gland, decreased adrenal gland sensitivity, impaired pituitary-adrenal stress responses, and reductions in both food intake and body weight. In addition, a threefold increase in diuresis was observed followed by a 1.5-fold increase in water intake; these latter effects were abolished by adrenalectomy. Together, these findings indicate that Ex-4 induces a profound dysregulation of HPA axis activity that may also affect renal function.

Central stress-integrative circuits: forebrain glutamatergic and GABAergic projections to the dorsomedial hypothalamus, medial preoptic area, and bed nucleus of the stria terminalis

Central regulation of hypothalamo-pituitary-adrenocortical (HPA) axis stress responses is mediated by a relatively circumscribed group of projections to the paraventricular hypothalamus (PVN). The dorsomedial hypothalamus (DMH), medial preoptic area (mPOA), and bed nucleus of the stria terminalis (BST) provide direct, predominantly inhibitory, innervation of the PVN. These PVN-projecting neurons are controlled by descending information from limbic forebrain structures, including the prefrontal cortex, amygdala, hippocampus, and septum. The neurochemical phenotype of limbic circuits targeting PVN relays has not been systematically analyzed. The current study combined retrograde tracing and immunohistochemistry/in situ hybridization to identify the specific sites of glutamatergic and GABAergic inputs to the DMH, mPOA, and BST. Following Fluoro-gold (FG) injections in the DMH, retrogradely labeled cells co-localized with vesicular glutamate transporter mRNA in the prefrontal cortex, ventral hippocampus, and paraventricular thalamus. Co-localization of FG and glutamic acid decarboxylase mRNA was present throughout the central and medial amygdaloid nuclei and septal area. In addition, the mPOA received predominantly GABAergic input from the septum, amygdala, and BST. The BST received glutamatergic projections from the hippocampus and basomedial amygdala, whereas, GABAergic inputs arose from central and medial amygdaloid nuclei. Thus, discrete sets of neurons in the hypothalamus and BST are positioned to summate limbic inputs into PVN regulation and may play a role in HPA dysfunction and stress-related illness.

Sexual dimorphism of stress response and immune/ inflammatory reaction: the corticotropin releasing hormone perspective

This review higlghts key aspects of corticotropin releasing hormone (CRH) biology of potential relevance to the sexual dimorphism of the stress response and immune/inflammatory reaction, and introduces two important new concepts based on the regulatory potential of the human (h) CRH gene: (1) a proposed mechanism to account for the tissue-specific antithetical responses of hCRH gene expression to glucocorticolds, that may also explain the frequently observed antithetical effects of chronic glucocorticoid administration in clinical practice and (2) a heuristic diagram to illustrate the proposed modulation of the stress response and immune/ inflammatory reaction by steroid hormones, from the perspective of the CRH system.

Acute restraint stress increases intrahypothalamic oestradiol concentrations in conjunction with increased hypothalamic oestrogen receptor β and aromatase mRNA expression in female rats

Activation of the hypothalamic-pituitary-adrenal axis is considered to be one of the key physiological responses to stress and, interestingly, shows a marked sex difference. Oestradiol plays an important role in this sex difference. The present study investigated the systemic and intrahypothalamic oestradiol response to physical restraint stress in female rats. We used jugular catheterisation and intrahypothalamic microdialysis to simultaneously measure plasma oestradiol and local oestradiol concentrations in the paraventricular nucleus (PVN) of the hypothalamus. We also assessed corticotrophin-releasing hormone (CRH), aromatase, and oestrogen receptor (ER) α and β mRNA expression in the PVN by quantitative polymerase chain reaction immediately after the acute stress period. As expected, PVN CRH mRNA and plasma corticosterone were significantly increased after acute stress. Interestingly, the local oestradiol concentration in the PVN also increased during the 1-h stress period in pro-oestrus and in ovariectomised (OVX) animals. Aromatase mRNA expression in the PVN was increased markedly in pro-oestrus but only modestly in oestrus. PVN ERβ but not ERα mRNA expression was significantly elevated in pro-oestrous animals. In addition, plasma oestradiol levels increased 10 min after stress, both during pro-oestrus and oestrus but not in OVX animals. To conclude, we report an intra-hypothalamic oestradiol response to restraint stress. The rising hypothalamic oestradiol concentration together with increased ERβ gene expression indicates a positive feedback of hypothalamic oestradiol signalling during acute stress in rats.

Fasting differentially modulates the immunological system: its mechanism and sex difference

The immunological properties and hormonal metabolism in rodents are affected by physical and psychological stress more strongly in males than in females. To elucidate the mechanism and physiological significance of the sex difference in the susceptibility of animal to stresses, changes in the immunological system in plasma and intestine and hormonal status in plasma were compared among 8-week-old male and female ICR mice before and after fasting. During the fasting of animals, the expression of immunoglobulin A in intestinal mucosa, and cortisol, interleukin-10 and interferon-gamma in plasma increased. These changes occurred more apparently in males than in females. Under identical conditions, the plasma levels of testosterone decreased markedly with concomitant occurrence of apoptosis in the testis, while the plasma levels of estradiol decreased calmly, and no appreciable apoptosis occurred in the ovary. These results indicate that testosterone enhances the stress-induced modulation of the immune system by some mechanism that was antagonized by estradiol.

Intrahypothalamic neuroendocrine actions of corticotropin-releasing factor

Most studies of the neuroendocrine effects of corticotropin-releasing factor (CRF) have focused on its role in the regulation of the pituitary-adrenal axis; activation of this axis follows release of the peptide from CRF-containing terminals in the median eminence. However, a sizeable proportion of CRF fibres terminate within the hypothalamus itself, where synaptic contacts with other hypothalamic neuropeptidergic neurons (e.g. gonadotropin-releasing hormone-containing and opioidergic neurons) have been identified. Here, we summarize physiological and pharmacological data which provide insights into the nature and significance of these intrahypothalamic connections. It is now clear that CRF is a potent secretagogue of the three major endogenous opioid peptides (beta-endorphin, Met-enkephalin and dynorphin) and that it stimulates opioidergic neurons tonically. In the case of beta-endorphin, another hypothalamic peptide, arginine vasopressin, appears to be an essential mediator of CRF's effect, suggesting the occurrence of CRF synapses on, or in the vicinity of, vasopressin neurons; morphological support for this assumption is still wanting. Evidence for direct and indirect inhibitory effects of CRF on sexual behaviour and secretion of reproductive hormones is also presented; the indirect pathways include opioidergic neurons. An important conclusion from all these studies is that, in addition to its better known functions in producing adaptive responses during stressful situations, CRF might also contribute to the coordinated functioning of various components of the neuroendocrine system under basal conditions. Although feedback regulation of hypothalamic neuronal activity by peripheral steroids is a well-established tenet of endocrinology, data on modulation of the intrahypothalamic actions of CRF by adrenal and sex steroids are just emerging. Some of these newer findings may be useful in framing questions related to the mechanisms underlying disease states (such as depressive illness) in which CRF has been strongly implicated.

Coat condition, housing condition and measurement of faecal cortisol metabolites - a non-invasive study about alopecia in captive rhesus macaques (Macaca mulatta)

BACKGROUND

Previous studies have characterized alopecia in captive rhesus macaques (Macaca mulatta) by a mixed partial to complete alopecia in a bilateral symmetric pattern.

METHODS

In this study, coat condition assessments were related to exogenous and endogenous factors in captive rhesus macaques under different housing conditions in order to identify disturbances in environmental factors controlling or influencing hair growth. Additionally, the degree of alopecia was investigated in relation to adrenal endocrine function as an indicator of social stress using faecal glucocorticoid measurements.

RESULTS

Hair loss was found to vary with season and sex, was most pronounced in adult females during the winter and spring months. Generally, infants were not affected, but alopecia developed during adolescence. However, the housing system, available enclosure space and variations in group size and composition also appeared to influence coat condition. Levels of immunoreactive cortisol metabolites (11-oxoetiocholanolone) in faeces were significantly negatively correlated with alopecia, suggesting a relationship between hypothalamic-pituitary-adrenal (HPA) axis activity and hair loss in captive rhesus macaques.

CONCLUSIONS

Although the present study demonstrates the influence of the HPA axis on coat condition, it is not known if hair loss is caused by abnormal behaviour or hormonal imbalances of the HPA axis itself. Our data suggest that alopecia in rhesus macaques is a highly complex multicausal disorder.

DHEA, PREG and their sulphate derivatives on plasma and brain after CRH and ACTH administration

The term neurosteroids applies to steroids that are synthesized in the nervous system, either de novo from cholesterol or from steroid hormone precursors. RIA was used to determine plasma and brain levels of the neurosteroids pregnenolone (PREG), dehydroepiandrosterone (DHEA), and their sulfate derivatives (PREG-S and DHEA-S) in male and female rats after administration of two typical stress hormones: corticotropin-releasing hormone (CRH) and adrenocorticotropin hormone (ACTH). In all cases, the parameters measured were detectable in plasma and brain. PREG, PREG-S, and DHEA increased significantly in plasma and brain after CRH and ACTH administration in males and females. Because neurosteroids play an important role in mammalian physiology, including that of humans, stress situations may alter the physiological functions regulated by these neurosteroids.

Gonadal hormone-induced changes in adult male and female rats exposed to early postnatal handling are not altered by prenatal morphine exposure

The purpose of the present study was to investigate the long-term effects of early postnatal handling in several gonadal hormone conditions in adult male and female rats exposed prenatally to morphine or saline. An open-field apparatus was used to test locomotor activities such as line crossing, rearing, grooming, and anxiety-like behaviors such as visiting squares alongside the walls of the open field and boli dropping. Postnatal handling increased locomotor activities in gonadally intact males and in all groups of hormone-manipulated females, but did not change them in gonadectomized (GNX) males. Additionally, there was a decrease in anxiety-like behavior in ovariectomized (OVX) females after estradiol benzoate (EB) or EB and progesterone (P) replacement due to handling. Handling did not affect anxiety-like behaviors in OVX females or in GNX or gonadally intact males. Prenatal morphine exposure did not alter any open-field measures in handled or nonhandled animals when compared to saline controls. Thus, the present study demonstrates that early postnatal handling induces long-lasting changes in locomotor and anxiety-like behaviors of adult male and female rats regardless of their prenatal exposure to morphine. These changes are gonadal hormone specific.

Corticosterone exerts site-specific and state-dependent effects in prefrontal cortex and amygdala on regulation of adrenocorticotropic hormone, insulin and fat depots

Chronic stress stimulates corticosterone secretion and recruits brain pathways that regulate energy balance (caloric acquisition and deposition) and facilitate hypothalamic-pituitary-adrenal responsiveness to new stressors. We implanted corticosterone or cholesterol bilaterally either near the central nucleus of the amygdala (CeA) or in the prefrontal cortex to determine whether high concentrations of the steroid act at either site, with or without chronic stress. Rats were adrenalectomized and treated systemically with low doses of corticosterone. Half were maintained at room temperature and the other half were exposed to 5 degrees C cold for 5 days before all rats were restrained. There was limited diffusion of corticosterone from brain implants. Corticosterone in prefrontal cortex, but not CeA, decreased plasma insulin and adrenocorticotropic hormone (ACTH) responses to acute restraint in both control and chronically cold stressed rats. Corticosterone implants near CeA decreased the weight of fat depots only in cold; corticosterone implants in prefrontal cortex were ineffective. We conclude that (i) corticosterone inhibits insulin and ACTH secretion by an action in prefrontal cortex but not CeA; (ii) high concentrations of corticosterone secreted during chronic stress alter metabolism through (autonomic) outputs of the CeA and prefrontal cortex in site- and variable-specific fashion; and (iii) the amygdala is a component of a stress-recruited, state-dependent pathway.

Effects of CRH and ACTH administration on plasma and brain neurosteroid levels

The 3alpha-hydroxy ring A-reduced metabolite of progesterone, 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) is among the most potent known ligands of the gamma aminobutyric acid (GABA) receptor, designated GABA-A, in the central nervous system. We determined by RIA serum levels of progesterone (PROG), 5-alpha-dihidroprogesterone (DHP) and allopregnanolone in male and female rats after corticotropin releasing hormone (CRH) and adrenocorticotropin hormone (ACTH) administration. Allopregnanolone was undetectable in plasma and brain of control males but detectable in plasma and brain of males injected with CRH and ACTH and of control and similarly treated females. Allopregnanolone increased in the plasma and brain after CRH and ACTH administration in all cases. The data demonstrate that the administration of CRH plus ACTH results in a rapid increase of the neuroactive steroid allopregnanolone in the brain of males and females to levels known to modulate GABA-A receptor function. Thus, stress could regulate neurosteroid biosynthesis via the hormones ACTH and CRH.

Influence of thiouracil-induced hypothyroidism on adrenal and gonadal functions in adult female rats

The effect of hypothyroidism on adrenals and gonads in adult female rats was investigated throughout the estrous cycle. Hypothyroidism was induced by administration of 4-Methyl-2-Thiouracil (Thiouracil) in the drinking water. The weight of ovaries and adrenals, and the plasma levels of corticosterone decreased in hypothyroid rats as compared with euthyroid rats throughout the estrous cycle. Hypothyroidism resulted in decreased concentrations of plasma LH on the day of diestrus and proestrus, whereas the plasma concentrations of prolactin and progesterone increased as compared with euthyroid rats. The weight of uteri and plasma concentrations of estradiol decreased during the day of diestrus and proestrus in hypothyroid rats as compared with euthyroid rats. To further clarify the dysfunction of hypothalamo-hypophysial-adrenal axis in hypothyroid rats, animals were stressed by immobilization for 3 hr. In hypothyroid rats, a marked increase in plasma levels of ACTH in response to immobilization stress was observed compared to euthyroid control, whereas increases in plasma concentrations of corticosterone were much smaller in hypothyroid than euthyroid rats. These results clearly indicate that hypothyroidism causes both gonadal and adrenal disturbances in adult female rats. The increased concentrations of plasma progesterone may be due to hypersecretion of prolactin during the day of proestrus and estrus, which in turn result in disruption of the estrous cycle.

Caloric restriction as a mechanism mediating resistance to environmental disease

It has been observed that susceptibility to many degenerative diseases increases concurrently with industrialization and rising living standards. Although epidemiologic studies suggest that specific environmental and dietary factors may be important, caloric intake alone (as reflected in body size) may account for much of the differential risk observed among diverse human populations. It has been suggested from animal studies that caloric intake may be the primary effector for many hormonal, metabolic, physiologic, and behavioral responses that coordinate reproductive strategy to apparent availability of food. When caloric intake is excessive, particularly at critical developmental stages, physiologic priorities are set for body growth and fecundity rather than for endurance and longevity. The converse occurs during periods of famine, thus increasing the probability that sufficient individuals survive to restore the population when conditions improve. Calorically restricted rodents have significantly longer reproductive and total life spans than their ad libitum-fed controls and exhibit a spectrum of biochemical and physiologic alterations that characterize their adaptation to reduced intake. These include reduced stature, hypercorticism in the absence of elevated adrenocorticotropic hormone levels, increased metabolic efficiency, decreased mitogenic response coupled with increased rates of apoptosis, reduced inflammatory response, induction of stress proteins and DNA repair enzymes, altered drug-metabolizing enzyme expression, and modified cell-mediated immune function. The overall profile of these changes is one of improved defense against environmental stress. This has been suggested as the mechanistic basis for the protective effects of low body weight on radiation and chemically induced cancers in experimental animals. It may also explain the significantly higher thresholds of acute toxicity observed when calorically restricted rodents are exposed to certain test compounds.

Adrenal axis activation by chronic social stress fails to inhibit gonadal function in male rats

Stress in males via the hypothalamic-pituitary-adrenal (HPA) axis may set into motion varied physiological alterations, including dysfunction of the hypothalamic-pituitary-gonadal (HPG) axis. However, the influence of the HPA on the HPG axis may not always be inhibitory. Presence or absence of stimuli of sexual significance that typically activates the HPG axis may alter the influence of the adrenal axis on gonadal axes. In this project, we used male rats and chronic social stimulation that included brief or extended periods with female rats to examine HPA-HPG axes interactions. In experiment 1, we used intact males and a 'chronic social stress' paradigm developed in our previous research that induces social instability by daily changing the membership of group-housed males with females. Thymus weight was reduced and corticosterone levels were marginally increased by chronic social stress, indicating a HPA axis hyperactivity. The HPG axis was also activated as shown by the increased weight of the androgen-sensitive sex structures. These results indicate that when these two axes are stimulated together, neither interferes with nor suppresses activities of the other. Implants of corticosterone pellets to adrenalectomized animals that maintained constant, high corticosterone levels failed to reverse the gonadal hyperactivity induced by sexual stimulation. In a second experiment, we studied the influence of different intensity of sexual stimulations on HPA-HPG axes interactions. Increased corticosterone levels and adrenal weight, indicating a HPA hyperactivity, failed to inhibit HPG hyperactivity as measured by the increased sexual organs weight, whatever the sexual intensity of the stimulation. This work demonstrates that the gonadal axis is freed from suppression when sexual stimulation occurs together with stress. The general conclusion is that the nature of complex social settings is important in determining interactions between the two neuroendocrine axes.

Concomitant infusion of ovine corticotropin-releasing hormone does not prevent suppression of the hypothalamus-pituitary-adrenal axis by dexamethasone in male rats

Glucocorticoids (GCs) suppress the hypothalamus-pituitary-adrenal (HPA) axis at various sites including hypothalamus, pituitary and extrahypothalamic brain. Previous studies have shown that corticotropin-releasing hormone (CRH) and vasopressin facilitate the recovery of HPA axis suppressed by GCs. In this study, we investigate whether the concomitant continuous infusion of CRH may prevent the suppression of HPA axis by GCs. Groups of male Wistar rats weighing 140 to 160 g were implanted subcutaneously with Alzet osmotic pump for delivery of dexamethasone (DEX), 2 micrograms/h and/or CRH, 0.66 microgram/h. Control rats were implanted with sialistic tube of similar size. Rats were decapitated 3 or 7 days after osmotic pump implantation. In spite of the suppression of plasma corticosterone, the body weight (BW), adrenal weight (AW), plasma corticotropin (ACTH) and pituitary ACTH content of rats treated with DEX for 3 days were not significantly different from those of control rats. Concomitant infusion of ovine CRH (oCRH) and DEX for 3 days caused impaired BW gain, adrenal atrophy in addition to further reduction of plasma corticosterone. Treatment with DEX and/or oCRH for 7 days caused further suppression of HPA axis as shown by reduced pituitary ACTH content. In conclusion, simultaneous infusion of oCRH and DEX does not prevent and may even worsen HPA axis suppression by DEX.

Dopamine infusion enhances the adrenocorticotropic hormone and cortisol response to metoclopramide in hyperprolactinemic patients but not in normal subjects

Based on the facts that prolactin and adrenocorticotropic hormone (ACTH) each seem to influence the secretion of the other, that dopamine is the established inhibitory factor for prolactin secretion and negatively modulates ACTH release, and finally that alterations of the central dopaminergic tone have been postulated in tumorous hyperprolactinemia, we studied the effects of pharmacological manipulations of the dopaminergic system on ACTH and cortisol secretion in patients bearing a prolactinoma and in normal subjects. Twenty-seven patients with a prolactin-secreting pituitary tumor and 12 healthy controls were submitted to three tests: (a) 4-h saline infusion; (b) 10 mg metoclopramide (MTC) as an intravenous bolus after a 2-h saline infusion; and (c) 4-h dopamine infusion at the dose of 0.01 microgram/kg/min with a 10-mg intravenous bolus of MTC given at the second hour of dopamine infusion. Administration of MTC, compared to saline, caused a moderate (not significant) plasma ACTH increase, and a significant cortisol increase (p < 0.05), both in hyperprolactinemic and normal subjects, without statistically significant differences between the two group. When MTC was administered during dopamine infusion, the ACTH and cortisol elevation was significantly potentiated in prolactinoma patients while it was similar in magnitude to that recorded after MTC alone in control subjects. These findings support the concept of an inhibitory role exerted by dopamine and are compatible with a stimulatory influence exerted by prolactin on corticotropin-releasing hormone and ACTH secretion, and also favor the view of a reduced central dopaminergic tone in patients with tumorous hyperprolactinemia.

Effects of repeated ether stress on the hypothalamic-pituitary-testes axis in adult rats with special reference to inhibin secretion

Effects of ether stress on the hypothalamo-hypophysial-gonadal axis in adult male rats were examined. To clarify the role of adrenal glucocorticoids in gonadal function, the effects of adrenalectomy and Dexamethasone treatment were also investigated. Ether stress increased the plasma concentrations of ACTH and corticosterone, but decreased the plasma concentrations of LH, FSH, inhibin and testosterone. The pituitary responsiveness to LH-RH for LH release and testicular responsiveness to the endogenous LH for testosterone release were maintained in stressed rats. Adrenalectomy caused an increase in the plasma concentrations of ACTH, but decreased the plasma concentrations of LH, FSH and testosterone. Dexamethasone treatment in adrenalectomized rats recovered the levels of plasma gonadotropins to control levels. The concentration of plasma inhibin did not change in adrenalectomized rats, but it was decreased compared to control rats by Dexamethasone treatment. Treatments of Dexamethasone in intact male rats resulted in a decline in plasma levels of testosterone and inhibin without a decrease in the levels of LH and FSH, indicating the direct effect of Dexamethasone on the testes. These results indicate that increased ACTH secretion in stressed rats is probably due to hypersecretion of CRH from the hypothalamus, which suppresses gonadotropin secretion via the inhibition of LH-RH. The decreased levels of testosterone may be caused by a stress-induced decrease in plasma LH concentrations and increased secretion of corticosterone in the ether stressed rats. The low levels of plasma inhibin in stressed rats was also probably due to the direct effect of corticosterone on the Sertoli cells.

Effect of corticotropin releasing factor (CRF) injected into the median eminence on LH secretion in male rats

We determined the dose-response relationship and examined the time-related effect of CRF (corticotropin releasing factor) injected directly into the Median Eminence (ME) on LH secretion in conscious intact and castrated male rats. Doses of 0.25, 0.75, 1, and 1.5 nmol CRF dissolved in 1 microl of saline (or saline only in the controls) were injected into the ME and blood samples collected 30, 60, 90, and 120 min postinjection to determine by RIA serum LH. CRF at doses of 0.75, 1 and 1.5 nmol significantly decreased serum LH in castrated and intact animals. The lower dose of CRF did not decrease LH in the two groups studied. The results suggest that in males as in females, CRF inhibits by itself LH secretion, at least in part, by a central action in the ME; the inhibitory effect of CRF on LH is similar in castrated and intact males; the dose of 0.25 nmoles of CRF was ineffective in decreasing LH and finally that CRF at ME levels may participate in a variety of stress-related responses, including reproduction inhibition, through LH suppression.

Corticotropin-releasing factor receptors: physiology, pharmacology, biochemistry and role in central nervous system and immune disorders

Corticotropin-releasing factor (CRF) plays a major role in coordinating the endocrine, autonomic, behavioral and immune responses to stress through actions in the brain and the periphery. CRF receptors identified in brain, pituitary and spleen have comparable kinetic and pharmacological characteristics, guanine nucleotide sensitivity and adenylate cyclase-stimulating activity. Differences were observed in the molecular mass of the CRF receptor complex between the brain (58,000 Da) and the pituitary and spleen (75,000 Da), which appeared to be due to differential glycosylation of the receptor proteins. The recently cloned CRF receptor in the pituitary and the brain (designated as CRF1) encodes a 415 amino acid protein comprising seven putative membrane-spanning domains and is structurally related to the calcitonin/vasoactive intestinal peptide/growth hormone-releasing hormone subfamily of G-protein-coupled receptors. A second member of the CRF receptor family encoding a 411 amino acid rat brain protein with approximately 70% homology to CRF1 has recently been identified (designated as CRF2); there exists an additional splice variant of the CRF2 receptor with a different N-terminal domain encoding a protein of 431 amino acids. In autoradiographic studies, CRF receptors were localized in highest densities in the anterior and intermediate lobes of the pituitary gland, olfactory bulb, cerebral cortex, amygdala, cerebellum and the macrophage-enriched zones and red pulp regions of the spleen. CRF can modulate the number of CRF receptors in a reciprocal manner. For example, stress and adrenalectomy increase hypothalamic CRF secretion which, in turn, down-regulates CRF receptors in the anterior pituitary. CRF receptors in the brain and pituitary are also altered as a consequence of the development and aging processes. In addition to a physiological role for CRF in integrating the responses of the brain, endocrine and immune systems to physiological, psychological and immunological stimuli, recent clinical data implicate CRF in the etiology and pathophysiology of various endocrine, psychiatric, neurologic and inflammatory illnesses. Hypersecretion of CRF in the brain may contribute to the symptomatology seen in neuropsychiatric disorders, such as depression, anxiety-related disorders and anorexia nervosa. Furthermore, overproduction of CRF at peripheral inflammatory sites, such as synovial joints may contribute to autoimmune diseases such as rheumatoid arthritis. In contrast, deficits in brain CRF are apparent in neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease and Huntington's disease, as they relate to dysfunction of CRF neurons in the brain areas affected in the particular disorder. Strategies directed at developing CRF-related agents may hold promise for novel therapies for the treatment of these various disorders.

Adrenal weight and morphology in victims of completed suicide

Several lines of evidence have implicated hypothalamic-pituitary-adrenal (HPA) axis dysfunction in major depression and suicidal behavior. In the present study, the weight and morphology of postmortem adrenal glands were compared between suicide victims and sudden death, nonpsychiatric controls. The mean adrenal weight of the combined left and right glands was significantly higher in the suicide group; this difference was accounted for specifically by increases in left adrenal weight of suicides compared with the control group. There was a positive correlation between adrenal weight and total cortical thickness in both left and right glands, providing direct evidence that increased adrenal weight in suicide victims is due to cortical hypertrophy. The finding of left-right adrenal weight asymmetry in suicides is consistent with the hypothesis of abnormal lateralized input from higher control centers of the HPA axis.

Androgen regulation of adrenocorticotropin and corticosterone secretion in the male rat following novelty and foot shock stressors

To examine mechanisms responsible for sex differences in hypothalamo-pituitary-adrenal (HPA) axis responsiveness to stress, we studied the role of androgens in the regulation of the adrenocorticotropin (ACTH) and corticosterone (CORT) responses to foot shock and novelty stressors in gonadectomized (GDX) or intact male F344 rats. Foot shock or exposure to a novel open field increased plasma ACTH and CORT, which was significantly greater in GDX vs. intacts. Testosterone (T) or dihydrotestosterone propionate (DHT) treatment of GDX animals returned poststress levels of ACTH and CORT to intact levels. Estrogen treatment of GDX males further increased poststress CORT secretion above GDX levels. There was no difference in the ACTH response of anterior pituitaries from intact, GDX, and GDX+DHT animals to CRF using an in vitro perifusion system. There were no differences in beta max or binding affinity of type I or II CORT receptors in the hypothalamus or hippocampus of intact, GDX, or GDX+DHT groups. These data demonstrate an effect of GDX on hormonal indices of stress. The increased response in GDX rats appears to be due to the release from androgen receptor mediated inhibition of the HPA axis. This inhibition by androgen is not due to changes in anterior pituitary sensitivity to CRH, nor to changes in type I or type II corticosteroid receptor concentrations.

Evidence of direct estrogenic regulation of human corticotropin-releasing hormone gene expression. Potential implications for the sexual dimophism of the stress response and immune/inflammatory reaction

Corticotropin-releasing hormone (CRH) plays major roles in coordination of the stress response and regulation of the immune/inflammatory reaction, two important functions associated with sexual dimorphism. Two overlapping segments of the 5' flanking region of the human (h) CRH gene, the proximal 0.9 kb (containing two perfect half-palindromic estrogen-responsive elements [EREs]) and the 2.4 kb (including the former and containing two additional perfect half-palindromic EREs), were examined for their ability to confer estrogen-mediated transcriptional enhancement to a homologous or heterologous promoter. The level of estrogen-induced transactivation by the 0.9- and 2.4-kb segments was determined by chloramphenicol acetyltransferase analysis in CV-1 cells cotransfected with estrogen receptor (ER) cDNA expression plasmids, and found to be respectively approximately 10% and 20% of that of the strongly estrogen-responsive Xenopus vitellogenin A2 enhancer. Gel retardation and immunoprecipitation demonstrated specific association between the perfect half-palindromic EREs of hCRH gene and the DNA binding domain of hER in vitro. These findings may constitute the basis of sexual dimorphism in the expression of the CRH gene in the central nervous system and periphery, and might shed light in existing gender differences in stress response and immune regulation.

Involvement of central corticotropin-releasing factor (CRF) in suckling-induced inhibition of luteinizing hormone secretion in lactating rats

The lack of ovulation and the inhibition of reproductive functions observed in many species during lactation is closely related to the intensity of the suckling stimulus. However, the mechanisms by which suckling inhibits hypothalamic GnRH and pituitary LH secretion in rats are still unclear. Since we recently demonstrated that suckling is a persistent stimulus to the adrenococortical system of the rat, we tested the hypothesis that suckling-induced activation of central CRF release may mediate the associated inhibition of GnRH secretion. Lactating females were ovariectomized (OVX) on day 2 of lactation, and equipped with icv guide cannula on day 2 and indwelling jugular catheters on day 5 before testing on day 7. Lactating females were separated from their pups for 24 h prior to the suckling test with the following pretreatments: 1) icv injection with artificial CSF (aCSF) or a specific CRF antagonist, alpha-helical CRF (9-41), (25 micrograms/rat, CRF-AX) 15 min prior to pup reunion or 2) iv injection of normal sheep serum (NSS) or CRF antiserum (CRF-AB) 4 h prior to pup reunion. Plasma ACTH, LH and PRL concentrations were determined prior to and at various intervals after pup reunion. After 3 h of suckling, LH and PRL responses to a bolus injection of GnRH (10 ng/rat) were measured; a bolus injection of Angiotensin II (AII, 5 micrograms/rat) was administered after 4 h to test for ACTH responses. Non-lactating females injected with GnRH and AII were used as controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 beta inhibits the endogenous expression of the early gene c-fos located within the nucleus of LH-RH neurons and interferes with hypothalamic LH-RH release during proestrus in the rat

The ability of central interleukin-1 beta (IL-1 beta) administration to modulate the hypothalamic LH-RH release as well as the endogenous expression of the c-fos protein located within the nucleus of LH-RH neurons was examined during the afternoon of proestrus in rats. In a first series of experiments, 50 or 100 ng IL-1 beta were infused into the lateral ventricle of the rat brain at either 08.30, 12.00, 14.30, or 17.00 h of proestrus. The animals were then perfused transcardially with a solution of 4% paraformaldehyde from 17.30 and 18.00 h. In a second series of experiments, the rats were equipped with an intracerebroventricular (i.c.v.) cannula in the lateral ventricle and a push-pull cannula into the median eminence (ME), and LH-RH secretion was measured during the afternoon of proestrus. The third experiment investigated the putative role of corticotropin-releasing factor (CRF) in modulating the inhibitory effect of IL-1 beta on LH secretion by infusing CRF antagonists before the i.c.v. administration of the cytokine to gonadectomized male and female rats. The central infusion of 50 or 100 ng IL-1 beta at 12.00 h completely blocked the spontaneous expression of c-fos protein which normally occurs in the nucleus of LH-RH neurons between 17.30 and 18.00 h on proestrus. In contrast, 50 ng IL-1 beta was less effective (P < 0.05) when administered at 08.30 h, and totally without effect when infused at 14.30 h. Infusion of 50 ng IL-1 beta also markedly suppressed the hypothalamic release of LH-RH in proestrus rats bearing a push-pull cannula into the ME, and significantly decreased plasma LH levels in both gonadectomized male and female rats. Finally, we observed that the central administration of CRF antagonists did not modify the inhibitory effects of the cytokine on the activity of the hypothalamic-pituitary-gonadal (HPG) axis. These results provide the first direct evidence that IL-1 beta is a potent inhibitor of LH-RH neuronal activity during the proestrus LH surge in intact cycling rats. As central administration of this cytokine completely inhibited the endogenous expression of c-fos protein within the nucleus of LH-RH neurons, our findings also suggest that IL-1 beta acts at the level of LH-RH perikarya.

Seasonal changes in in vivo cortisol response to ACTH and in plasma and pituitary concentrations of ACTH in a desert rodent, the sand rat (Psammomys obesus)

1. During spring, decreased sensitivity of the adrenal cortex to adrenocorticotrophic hormone (ACTH) in the sand rat inhabiting the Béni-Abbès area (Algeria), results in a reduction in the production of cortisol. Thus the secretion of ACTH is enhanced, becoming maximal in June and presumably also during the following weeks. 2. Increase in ACTH secretion, together with a slightly increased adrenal sensitivity, is likely to stimulate corticosteroidogenesis throughout the summer. 3. In autumn, as levels of cortisol are high, the negative feedback increases leading to a reduction in ACTH production. 4. An increase in the adrenocortical sensitivity to ACTH allows a high production of cortisol until February.

Differential effects of central and peripheral injection of interleukin-1 beta on brain c-fos expression and neuroendocrine functions

Cytokines such as interleukin-1 beta (IL-1 beta) alter the activity of the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes in the rat. However, the brain sites at which IL-1 beta exerts these effects have not been well identified. The present study sought to identify some of these sites, using c-fos protein expression as an index of cellular activation. We also attempted to determine possible differences between the effects of peripheral and central injection of IL-1 beta on the activation of specific brain areas. Castrated male rats received intravenous (i.v.) or intracerebroventricular (i.c.v.) injections of IL-1 beta through a jugular catheter or a permanent cannula implanted in the right lateral ventricle, respectively. Blood samples were taken before, as well as 30 and 120 min after i.v. or i.c.v. IL-1 beta infusion in order to measure plasma ACTH and LH levels. Immediately thereafter, the rats were anesthetized with pentobarbital, then perfused. Their brains were removed and postfixed for one hour. Thirty-microns frozen sections were cut and approximately every fourth tissue section was processed for c-fos expression by an avidin-biotin-peroxidase method. Both i.v. (1 microgram) and i.c.v. (100 ng) injection of IL-1 beta significantly increased plasma ACTH levels, but only i.c.v. treatment measurably inhibited LH secretion. I.c.v. infusion of the cytokine markedly augmented c-fos expression in the paraventricular nucleus (PVN) and the arcuate nucleus (ARC) of the hypothalamus. A large amount of CRF cells in the PVN contained labelled c-fos protein (as measured by a double labelling technique), which indicates that CRF perikarya in this hypothalamic region are activated by the central administration of IL-1 beta. In contrast, i.v. injection of IL-1 beta did not significantly alter c-fos expression in the PVN or the ARC of the hypothalamus. These results suggest that the increased HPA axis activity which follows the peripheral IL-1 beta administration, a phenomenon previously shown to depend on endogenous CRF, does not require immediate activation of hypothalamic CRF perikarya. Thus our results indicate that the stimulatory effect of blood-born cytokine may be exerted at the level of nerve terminals in the median eminence. In contrast, i.c.v.-injected IL-1 beta appears to activate the HPA axis through a stimulation of CRF neurons within the parvocellular part of PVN.(ABSTRACT TRUNCATED AT 400 WORDS)

Negative Feedback by Corticosterone is the Major Mechanism Responsible for Corticotropin-Releasing Factor-Induced Desensitization

Abstract Subcutaneous infusion of ovine corticotropin-releasing factor (oCRF) to male rats at a rate of 0.1 mug/h for 4 days did not alter the rise of plasma adrenocorticotropin (ACTH) and corticosterone induced by 3-min ether exposure. In contrast, 1.0 mug/h oCRF for 4 days virtually abolished the ACTH response to ether, whereas a substantial corticosterone response was preserved. Intravenous administration of phenoxybenzamine (5 mg/kg) prior to ether stress completely inhibited the corticosterone response. Plasma ACTH and corticosterone responses in chronic CRF-treated rats to an intravenous bolus injection of 2.0 mug oCRF were also markedly blunted by pretreatment with subcutaneous oCRF 1.0 mug/h for 4 days. Adrenalectomized rats given corticosterone in the drinking fluid at a concentration of 80 mug/ml showed a plasma corticosterone pattern mimicking the normal diurnal rhythm. Basal plasma ACTH and thymus weight were within normal limits. In these rats, the magnitude of ACTH rise to ether stress did not differ between the chronic CRF-treated rats and the vehicle-treated rats. In cultured pituitary cells prepared from animals infused with oCRF 1.0 mug/h for 4 days, the basal and CRF-stimulated ACTH release was reduced by 46%. We conclude that among the possible mechanisms proposed for 'desensitization' during long-term infusion of CRF, negative feedback by elevated corticosterone at both brain and pituitary levels is the primary factor. The results also suggest the existence of non-ACTH-mediated catecholaminergic systems in the stress-induced adrenocortical activation.

Prolonged exposure to alcohol: effect on CRF mRNA levels, and CRF- and stress-induced ACTH secretion in the rat

We have conducted studies in intact adult male rats, designed to examine the effect of a 3- or 7-day exposure to alcohol (EtOH) on the pituitary's response to corticotropin-releasing hormone (CRF) or stress, and on CRF expression in the hypothalamus. In a first series of experiments, rats exposed to EtOH vapors for 7 days had mean blood alcohol levels (BAL) of 127 +/- 12 mg%. At the end of the 7-day period, basal plasma ACTH levels were 69 +/- 10 pg/ml in control rats and 121 +/- 23 pg/ml in EtOH animals (P less than or equal to 0.01). Resting corticosterone levels were 39 +/- 11 ng/ml in control animals, and 101 +/- 24 ng/ml in EtOH rats (P less than or equal to 0.01). In all experiments described here, there was no statistical difference (P greater than 0.05) between the body weights of controls (animals kept in chambers with normal atmosphere) and EtOH-exposed animals. In control animals, the injection of 0.3-10 micrograms ovine CRF per rat caused dose-related increases in plasma ACTH levels measured 10 min later. All doses of CRF also significantly (P less than or equal to 0.01) stimulated ACTH secretion by EtOH rats, but there was no clear dose-response curve. Though EtOH-treated animals responded to the lower dose of CRF (0.3 microgram) with larger increases in plasma ACTH levels than control rats, the only statistical difference (P less than or equal to 0.01) between control and EtOH rats was observed following administration of 10 micrograms CRF, which caused a blunted response in EtOH animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The anorectic effects of CRH and restraint stress decrease with repeated exposures

Intracerebroventricular (icv) administration of corticotropin-releasing hormone (CRH) or exposure to a restraint stressor causes acute anorexia in rats. However, the effects on food intake of repeated injections of CRH or repeated exposures to restraint stress have not been previously reported. As the effects of these more chronic CRH and stress treatments may be of greater relevance to emerging hypotheses of the pathogenesis of human eating and affective disorders, we measured the changes in food intake and body weight of rats after repeated central injections of CRH. In two experiments using two different daily dosages of CRH and two different schedules of administration, we found that the anorectic effect of CRH decreased over repeated injections. Weight gain was slowed significantly only in the high-dose experiment. Rats may become tolerant to the anorectic effects of CRH delivered by repeated icv injections. These findings have important implications for hypothesized mechanisms of anorexia nervosa and/or depression.

Regulation of the gonadotropin-releasing hormone (GnRH) neuronal system: morphological aspects

This paper gives a brief survey of the structural organization of the GnRH neuronal system and of the chemically identified axons impinging directly on GnRH neurons. There are great species differences in the localization of the GnRH nerve cells. In the human and monkey brain, they are concentrated in the medial basal hypothalamus. GnRH neurons project not only to the median eminence, but terminate also on other nerve cells including GnRH elements. Under physiological circumstances the GnRH neurons are influenced by nervous structures in- and outside the medial basal hypothalamus and by ovarian and other hormones. Recent, primarily immunocytochemical studies indicate that catecholaminergic, serotoninergic, GABA-ergic, opioid peptidergic, immunoreactive substance-P and corticotropin releasing factor-immunoreactive axons synapse on GnRH neurons. These findings provide morphological basis for the view that neurons operating with these compounds can act directly on GnRH release. Direct connections of the GnRH neurons demonstrated so far does not exclude the possibility that these neurotransmitters or neuromodulators influence GnRH release also at other levels of the CNS.

Estradiol or ovariectomy decreases CRF synthesis in hypothalamus

Gonadectomy and gonadectomy plus chronic estradiol administration decrease the content of hypothalamic corticotropin-releasing factor-like immunoreactivity (CRF-ir). This investigation was conducted to determine whether this was a result of chronic inhibition of CRF synthesis or stimulation of release. Administration of the protein synthesis inhibitor anisomycin one hour prior to sacrifice in otherwise untreated controls resulted in a 21% decrease in median eminence CRF-ir (p less than 0.01). Rats were ovariectomized and then administered either estradiol or vehicle daily for 3 weeks. Compared to vehicle-treated controls, estradiol treatment decreased CRF-ir in median eminence (p less than 0.01). In contrast to controls, administration of anisomycin to these ovariectomized rats did not significantly decrease median eminence CRF-ir in either the vehicle or estradiol-treated groups, implying that CRF synthesis was already depressed. Plasma adrenocorticotropin (ACTH) was increased by anisomycin treatment in all groups whether intact, ovariectomized or estradiol-treated (p less than 0.0005). Adrenal weights did not differ between these groups, or in comparison to sham-ovariectomized rats, indirectly implying lack of chronically elevated plasma ACTH. These data suggest that the mechanism for both the ovariectomy and chronic estradiol-induced decrease in CRF-ir content is an inhibition of CRF synthesis as opposed to a stimulation of CRF release.

Corticotropin-releasing factor stimulates the release of methionine-enkephalin and dynorphin from the neostriatum and globus pallidus of the rat: in vitro and in vivo studies

This study examined the changes in the in vitro and in vivo release of methionine-enkephalin (Met-enkephalin), and dynorphin from the rat neostriatum in response to corticotropin-releasing factor (CRF). The levels of each opioid peptide were measured in the same sample collected at each time interval by specific radioimmunoassay methods. The in vitro release experiments were conducted using neostriatal slices (250 microns) obtained from adult male Wistar rats whereas in the in vivo studies, the release of both Met-enkephalin and dynorphin were assessed in push-pull perfusates of the caudate nucleus (containing both Met-enkephalin and dynorphin cell bodies/fibres) and the globus pallidus (containing Met-enkephalin and dynorphin terminals) of chloral hydrate-anaesthetised adult male Wistar rats. In the in vitro studies, CRF (10(-12), 10(-10) and 10(-8) M) (applied in pulses of 75 min) stimulated both Met-enkephalin and dynorphin release from the neostriatal slices in a dose-related manner; in the presence of the CRF receptor antagonist, alpha-helical CRF9-41 (10(-6) M) the release of both Met-enkephalin and dynorphin in response to CRF (10(-8) M) were completely blocked. Push-pull perfusion experiments conducted in both the caudate nucleus and the globus pallidus, also demonstrated a dose-related increase in the release of both Met-enkephalin and dynorphin in response to CRF (10(-12), 10(-10) and 10(-8) M) applied in 60-min pulses. In addition, in each of the two brain sites, the release of both Met-enkephalin and dynorphin in response to CRF (10(-8) M) was completely blocked by alpha-helical CRF9-41 (10(-6) M). Both the in vitro and in vivo studies thus demonstrate that CRF can exert potent effects on Met-enkephalin and dynorphin release within the neostriatum-pallidum of the rat and that such effects are mediated via receptors specific for CRF, probably located on both the cell bodies and terminals of these opioid-containing neurones. The data obtained in this study thus substantiate the view that CRF, in addition to its regulation of pituitary opioid peptides, can communicate to opioid-containing neurones within the central nervous system and that many of the effects elicited by CRF may be ascribed to the opioid peptide released by CRF.(ABSTRACT TRUNCATED AT 400 WORDS)